Question

find dy/dx at x=0
y=u-(2/u)
u= (3x+1)^3

Answer 1

dy/du = 1+(2/u^2)

du/dx = 3*3(3x+1)^2

Answer 2

2 9(3x+1)^2
(1+ -------- ) * ( ---------)
(3x+1)^6 1

Answer 3

18(3x+1)^2
9(3x+1)^2 + ------------
(3x+1)^6



9(3x+1)^6 + 18
--------------- ??
(3x+1)^4

Answer 4

how did you get dy/du =u-(2/u)?

Answer 5

y = u -(2/u)

dy = 1 - (-2/u^2) du

dy/du = 1 + (2/u^2)

Answer 6

at x=0; id say that i did the calculation right and go with:

27

Answer 7

ohh got it! thanks!

Answer 8

you could simply plug the value of u into the equation for f(u)... but the chain rule makes life easier